Cryoprotectant composition

ABSTRACT

Aqueous plant cryoprotectant composition containing between about 0.005 and 25 wt. % tetrahydrofurfuryl alcohol, tetrahydrofurfuryl amine or mixtures thereof and method of increasing the resistance of plant tissue to damage caused by freezing conditions comprising applying to the plant tissue surfaces at ambient non-freezing temperatures an aqueous solution containing an effective amount of tetrahydrofurfuryl alcohol, tetrahydrofurfuryl amine or mixtures thereof.

This application is a division of U.S. patent application Ser. No.07/415,725, filed Oct. 2, 1989, now abandoned, which is a division ofSer. No. 07/216,126, filed Jul. 7, 1988, issued on Dec. 12, 1989 as U.S.Pat. No. 4,886,543.

BACKGROUND OF THE INVENTION

This invention relates to plant cryoprotectant compositions and methodsfor preventing damage to plants caused by exposure to freezingtemperatures for limited periods.

Freezing temperatures are a major cause of damage to plants and planttissue. According to one estimate, approximately $1.5 billion ofagricultural products are annually lost to freezing temperatures in theUnited States. In Florida alone, more than $3 billion of frost-damage tocitrus trees has been reported over the last five years.

Numerous methods have been attempted to prevent damage to plants andplant tissue caused by freezing temperatures. One such method involvesthe development of hardy plant species, a laborious, time consuming andcostly proposition. Other methods involve the use of fogs, smoke,protective foams, bags and the like to prevent the escape of heat fromthe plant. Still other methods involve the use of wind machines, heatersand/or irrigation. However, none of these approaches has proven to beboth effective and commercially practical.

A different approach that has been attempted to prevent frost damage toplants involves treatment of the plant with a cryoprotectantcomposition. During the last 75 years, many compounds have beenidentified which exert cryoprotection when added to plant tissues.However, in order to be practically useful, such a composition must benon-toxic to plants, environmentally acceptable and relativelyinexpensive. The center of research interest in this field has changedfrom early emphasis on small molecules that penetrate the cell, to morerecent exploration of protective effects derived from very largenon-penetrating compounds as they affect the properties of the externalsolution, However, none of these compounds are currently in wide-spreaduse. A few successful trial cases have been reported, but the chemicalsemployed have not been generally accepted.

SUMMARY OF THE INVENTION

Among the objects of the invention, therefore, may be noted theprovision of a plant cryoprotectant composition that increases thehardiness of plants and plant tissue, Another object of this inventionis the provision of a plant cryoprotectant composition which isrelatively inexpensive, non-toxic, and environmentally acceptable. Afurther object of this invention is the provision of a method for thecryoprotection of plants and plant tissue.

Briefly, therefore, the present invention is directed to an aqueousplant and plant tissue cryoprotectant solution containing between about0.005 and about 25 wt. % of a cryoprotectant component selected from thegroup consisting of tetrahydrofurfuryl alcohol, tetrahydrofurfuryl amineand mixtures thereof.

The invention is further directed to a method of increasing theresistance of plant tissue to damage caused by freezing conditionscomprising applying to the plant tissue surfaces at an ambientnon-freezing temperature, an aqueous solution containing between about0.005 and about 25 wt. % of a cryoprotectant component selected from thegroup consisting of tetrahydrofurfuryl alcohol, tetrahydrofurfuryl amineand mixtures thereof at least about 4 hours prior to the onset of suchfreezing conditions.

Other objects and features of this invention will be in part apparentand in part pointed out hereinafter.

DESCRIPTION OF THE INVENTION

In accordance with this invention, a plant cryoprotectant compositionhas been discovered which comprises an aqueous solution containing acryoprotectant component selected from the group consisting oftetrahydrofurfuryl alcohol, tetrahydrofurfuryl amine or mixturesthereof. Preferably, the composition comprises between about 0,005 andabout 25 wt% of the cryoprotectant component and most preferablycomprises between about 0.1 and about 5 wt% of the cryoprotectantcomponent,

Tetrahydrofurfuryl alcohol is a colorless, high boiling, primary alcoholhaving the following structure: ##STR1## Tetrahydrofurfuryl amine is acolorless, high boiling primary amine having the following structure:##STR2##

Although both tetrahydrofurfuryl alcohol and tetrahydrofurfuryl amineexhibit plant cryoprotectant properties, tetrahydrofurfuryl alcohol ispreferred in accordance with the present invention. Tetrahydrofurfurylalcohol is produced by hydrogenation of furfuryl alcohol and is marketedunder the name THFA. As expected on the basis of its structure,tetrahydrofurfuryl alcohol exhibits behavior characteristics of bothalcohols and ethers. Due to its cyclic ether structure,tetrahydrofurfuryl alcohol possesses distinctly unique solventproperties which are desirable for cryoprotecting agents, such as:

1. low volatility (vapor pressure 2.3 mm Hg at 39° C.),

2. non-damaging and non-toxic,

3. biodegradable,

4. easily absorbable,

5. ability to penetrate membranes,

6. considerable solubility in water in addition, to its ability to formmultiple hydrogen bonds,

7. ability to dissolve electrolytes.

The resistance of plants and plant tissue to frost and low temperatures,including subfreezing temperatures, are increased for limited periodsthrough the application of the cryoprotectant composition of thisinvention by spraying or dipping. For spraying, any suitable plant sprayapparatus suitable for spraying aqueous solutions may be employed. Theplants to be treated are thoroughly sprayed so that all of the planttissue surfaces are completely covered. Due to the size or shape of aplant, a single application may require two or more sprayings.

The cryoprotectant composition is applied at ambient, non-freezingtemperatures, i.e., the temperature of the air surrounding the plant orplant tissue is above 32` F. Preferably, the cryoprotectant compositionis applied when the ambient air temperature is at least 35° F.

The cryoprotectant composition may be formulated and supplied to theuser in concentrated form and diluted to the desired strength prior toapplication to the plant. No special handling or mixing steps arerequired. THFA and tetrahydrofurfuryl amine are stable in aqueoussolution. Moreover, these compositions are stable to light and do notneed to be stored in an opaque container nor prepared immediately priorto application.

Since an aqueous THFA or tetrahydrofurfuryl amine solution may notcompletely wet the surfaces of leaves of plants having waxy leaves, forsome applications it is preferred that the cryoprotectant compositioninclude a non-ionic surfactant. Two different surfactants,polyoxyethylene sorbitan monolaurate (Tween 20) and polyoxyethylenesorbitan monooleate (Tween 80) have been found to improve the wetabilityof the composition and thereby improve its effectiveness. When non-ionicsurfactants are used, it is preferred that the cryoprotectantcomposition contain between about 0.05 and about 0.5 wt. % non-ionicsurfactant.

The effectiveness of the cryoprotectant composition is not diminished bythe inclusion of such compounds as organic/inorganic fertilizers,pesticides, plant hormones, growth regulators, other polymers, andcoating materials. For instance, it has been found that the compositionis compatible with urea; the introduction of urea via a 1:1 THFA:UREAmixture, did not affect the wetability or the effectiveness of theagent. Nevertheless, it is presently preferred that the cryoprotectantcomposition have an essential absence of pesticides.

Although the cryoprotectant composition of this invention may be appliedto the plants immediately prior to exposure to freezing conditions, itis preferred that the composition be applied between about 4 hours and 1week prior thereto. Moreover, for optimal results it is preferred thatthe cryoprotectant composition be applied twice prior to the onset offreezing temperatures, the first application being made between aboutseveral days and about one week prior to the onset of freezingtemperatures and constituting a conditioning application. The secondapplication is then preferably made a sufficient period prior to theonset of freezing temperatures to permit absorption of the composition,e.g., at least about 4 hours.

For maximum protection during the spring frost season, it may bedesirable to apply the cryoprotectant composition weekly to minimize anydamage that might be caused by a sudden occurrence of freezingtemperatures. Nevertheless, due to this agent's high penetrability intosome plant tissues, it may be possible to apply this inventionimmediately before the exposure to freezing temperatures if the plantcan to tolerate a high concentration of the agent.

The following examples illustrate the invention. All percentages are byweight unless otherwise indicated.

EXAMPLE 1 A. Materials and Methods

Plants were sprayed with the indicated antifrost agents and set out atroom temperature for a period of time for conditioning. Several hoursprior to exposure to freezing temperatures, a second application of theantifrost agent was given to some of the plants. The period between thefirst application and the second application is referred to hereinafteras the conditioning time and the period between the second applicationand the placement in the freezer, as described below, is referred to asthe absorption time. For those instances in which there was only asingle application and the elapsed time between the application andplacement in the freezer exceeded 12 hours, that period is referred toas conditioning time. If the period was less than 12 hours, it isreferred to as absorption 5 time.

The pots holding the conditioned plants were fitted into a polyurethaneinsulated box having circular openings in the top. Each opening wassized to snugly receive a single pot holding a conditioned plant and thebox had sufficient depth so that substantially the entire pot wascontained within the insulated box while the conditioned plant stoodoutside the box. The box was heated by circulation of room temperatureair through its interior. The insulated box holding the plants wereplaced inside a commercial freezer that was modified to achieve dynamictemperature control to within 0.01° C. The air temperature inside thefreezer was monitored on a CRT screen and also recorded on a chartrecorder. The air temperature inside the freezer was gradually reduced(4° C./hr) from an initial temperature (10° C.) until the set pointtemperature was achieved. The set temperature was maintained for aperiod of three or four hours and then gradually warmed (4° C./hr) to afinal temperature (≧5° C.). During the period that the plant was insidethe freezer, the insulated box protected the roots from freezingsomewhat the same, but less efficiently, as the ground does in nature.

After removal from the freezer, the plants were inspected and a binaryresult recorded, i.e., either the plants survived or were permanentlydamaged. Visual observance could easily differentiate the effectivenessof the various antifrost agents tested. For each test, if all of theplants survived the initial cold, the plants were removed from thefreezer, the pots were allowed to return to room temperature and theplants were then returned to the freezer where the air temperature wasthen set at a lower temperature than the previous run. This process wasrepeated until a temperature was reached at which some of the plants didnot survive. The useable temperature range and relative effectiveness ofthe antifrost agents was thus determined.

The maximum time for exposure to freezing temperatures was limited to 6hours because beyond that, the pots could not be kept from freezing.Instead, the tests in which plants survived exposure for 6 hours wererepeated a few times to determine whether the plants could survivelonger exposure, like those encountered under actual conditions in thefield.

The antifrost agents evaluated were the following:

1. tetrahydrofurfuryl alcohol dissolved in deionized (DI) water to make0.5% and 5% THFA aqueous solutions;

2. 0.1 parts of a surfactant, polyoxyethylene sorbitan monolaurate(Tween 20) and 0.5 parts tetrahydrofurfuryl alcohol dissolved in 99.4parts DI water to make an aqueous 0.5% THFA +0.1% Tween 20 solution;

3. 0.5 parts urea and 0.5 parts tetrahydrofurfuryl alcohol dissolved in99 parts DI water to make an aqueous 0.5% THFA +0.5% urea solution.

4. polyethyleneglycol polysiloxane copolymer having a PG/PS monomerratio of 5.3/1 prepared according to the method set forth in D. J.Bannister, et al "Water Soluble Siloxane: Poly (Erthylene Glycol) CombPolymer", Journal of Polymer Science: Polymer Letters Ed., Vol. 23, p.465-467 (1985), dissolved in DI water to make aqueous 0.5% and 5% PS/PEGsolutions;

5. A non-ionic surfactant GOLDEN FROST FREE (Plant Products Corporation;Vero Beach Fla.), dissolved in DI water to make aqueous 0.3% and 0.29%Golden Frost Free solutions;

6. a polyoxyethylenated polyoxypropylene copolymer (molecular weight4500) obtained from Diamond Shamrock Corporation under the trademarkMonolan 4500, dissolved in DI water to make aqueous 0.3% and 0.4%solutions designated PPC707;

7. equal parts tetrahydrofurfuryl alcohol and polyethyleneglycolpolysiloxane copolymer (subpart 4, above) dissolved in DI water to makean aqueous 0.25% THFA +0.25% PS/PEG solution ("10.5% mixture");

8. tetrahydrofurfuryl amine dissolved in DI water to make an 0.5%tetrahydrofurfuryl aqueous solution.

9. furfuryl alcohol dissolved in DI water to make an 0.5% furfurylalcohol aqueous solution.

10. 1,2-propanediol dissolved in DI water to make an 0.5%1,2-propranediol aqueous solution.

B. Evaluation of the Antifros,4 Agents with Impatiens

Garden plants of the impatiens variety were sprayed with variousantifrost agents listed in part A (as indicated in Table I). Each plantwas treated twice with the respective antifrost agent and was allowedfive days between the two applications for conditioning. After thesecond spray, a six hour absorption period was provided. The plants werethen placed in the freezer and the temperature was lowered to the setpoint temperature (-3.5° C.), maintained there for three hours, and thenraised to 8° C. over a three hour period.

As shown in table I, the impatiens treated with 0.5% THFA and 0.5%PS/PEG survived whereas the plants treated with PPC707 and those exposedwithout any antifrost treatment died.

                  TABLE I                                                         ______________________________________                                        FREEZING DAMAGE TEST RESULTS FOR IMPATIENS                                    EXPOSED TO -3.5° C. FOR THREE HOURS                                                  Conditioning/Absorption                                         Antifrost Agent                                                                             Time              Results                                       ______________________________________                                        Blank         --/--             Died                                          0.5% PS/PEG   5 days/6 hours    Survived                                      0.5% THFA     5 days/6 hours    Survived                                      0.3% Golden Frost Free                                                                      5 days/6 hours    Died                                          0.3% PC707    5 days/6 hours    Died                                          ______________________________________                                    

10 C. Second Evaluation of the Antifrost Agents with Impatiens

The procedure provided in part B was repeated, except that some of theplants were given a single application of the compositions having ahigher concentration of the antifrost agents to determine whether theseagents are effective with only one treatment. The remainder of theplants were given two applications as indicated in Table II. The resultslisted in Table II indicate that impatiens treated once with either 5%PS/PEG or 5% THFA survived the freezing temperatures. Again, plantstreated with 0.5% PS/PEG or 0.5% THFA survived, while those treated withPPC707 or Golden Frost Free, like the ones left without any antifrostprotection, did not survive.

                  TABLE II                                                        ______________________________________                                        FROST DAMAGE TEST FOR IMPATIENS                                               EXPOSED TO -3.5° C. FOR THREE HOURS                                                   Conditioning/Absorption                                        Antifrost Agent                                                                              Time             Results                                       ______________________________________                                        Blank          --/--            Died                                          0.5% PS/PEG       --/6 hours    Died                                          5% PS/PEG         --/6 hours    Survived                                      5% PS/PEG      2 days/--        Survived                                      0.5% Mixture   5 days/6 hours   Survived                                      0.5% THFA      7 days/6 hours   Survived                                      5% THFA           --/6 hours    Survived                                      0.4% PPC707    7 days/6 hours   Died                                          0.29% Golden Frost Free                                                                      7 days/6 hours   Died                                          ______________________________________                                    

D. Evaluation of the Antifrost Agents with Fuchsias

The procedure in part B was repeated except that the garden plantsemployed for this test were fuchsias. The fuchsias were treated withvarious antifrost agents (as indicated in Table III) and then exposed toa freezing temperature of -4° C. for three hours. The test results inTable III show that Golden Frost Free, 0.5% THFA, 0.5% PS/PEG, and 5%THFA are effective in protecting fuchsias from the ravages of frost.

                  TABLE III                                                       ______________________________________                                        FROST DAMAGE TESTS FOR FUCHSIAS                                               EXPOSED TO -4° C. FOR THREE HOURS                                                     Conditioning/Absorption                                        Antifrost Agent                                                                              Time            Results                                        ______________________________________                                        Blank          --/--           Died                                           Golden Frost Free                                                                            5 days/4 hours  Survived                                       0.5% THFA      5 days/4 hours  Survived                                       0.5% PS/PEG    5 days/4 hours  Survived                                       5% THFA           --/4 hours   Survived                                       5% PS/PEG         --/4 hours   Died                                           ______________________________________                                    

E. Second Evaluation of the Antifrost Agents with Fuchsias

Freezing survival tests for fuchsias were repeated in the same manner asabove, except that the freezing temperature in this experiment wasmaintained at -5° C. for four hours. The results listed in Table IVindicate that PPC707, Golden Frost Free, and PS/PEG are not individuallyas effective as is THFA for fuchsias. Fuchsias treated with 5% THFA for4 hours prior to their exposure to -5° C. survived, as did those treatedtwice with 0.5% THFA. Fuchsias sprayed with 5% THFA for only 2 hoursprior to exposure for freezing conditions also survived.

                  TABLE IV                                                        ______________________________________                                        FREEZING SURVIVAL TESTS OF FUCHSIAS                                           TESTED AT -5° C. FOR FOUR HOURS                                                      Conditioning/Absorption                                         Antifrost Agent                                                                             Time             Results                                        ______________________________________                                        0.4% PPC707   7 days/4 hours   Died                                           0.4% Golden Frost Free                                                                      7 days/4 hours   Died                                           0.5% PS/PEG   7 days/4 hours   Died                                           0.5% Mixture  7 days/4 hours   Died                                           0.5% THFA     7 days/4 hours   Died                                           5% THFA          --/4 hours    Survived                                       5% THFA          --/2 hours    Survived                                       5% THFA       1 day/--         Survived                                       5% THFA       8 days/--        Survived                                       ______________________________________                                    

F. Third Evaluation of the Antifrost Agents with Fuchsias

Here, the freezing temperature was lowered to -6° C. and maintainedthere for 4 hours. The fuchsias tested in this example were those whichsurvived the previous freezing tests. The purpose of this test was todetermine whether the plants could survive longer exposures, like thoseencountered under actual conditions in the field.

                  TABLE V                                                         ______________________________________                                        FREEZING SURVIVAL TESTS                                                       FOR FUCHSIAS EXPOSED TO -6° C.                                         Antifrost Agent                                                                           Total Exposure Time                                                                             Results                                         ______________________________________                                        0.5% THFA    8 hours          Survived                                        0.5% THFA   12 hours          Survived                                        5% THFA      8 hours          Survived                                        5% THFA     12 hours          Survived                                        ______________________________________                                    

G. Evaluation of the Antifrost Agents with Coleuses

The garden plant coleus is very delicate and sensitive to freezingtemperatures due to the high water content of its tissues. A set of sixcoleuses treated with different antifrost agents was exposed to -7° C.for four hours. The results of this test are listed in Table VI. Theplants treated twice with 0.5% THFA survived. Coleuses treated with 5%THFA showed signs of antifrost agent rejection and were not included inthis frost survival test.

                  TABLE VI                                                        ______________________________________                                        FREEZING SURVIVAL TEST FOR COLEUSES EXPOSED                                   TO -7° C. FOR FOUR HOURS                                                            Conditioning/Absorption                                          Antifrost Agent                                                                            Time              Results                                        ______________________________________                                        Blank        --/--             Died                                           0.29% Golden Frost                                                                         3 days/2 hours    Died                                           Free                                                                          0.3% PPC707  3 days/2 hours    Died                                           0.5% Mixture 3 days/2 hours    Died                                           0.5% THFA    3 days/2 hours    Survived                                       0.5% THFA    3 days/2 hours    Survived                                       ______________________________________                                    

H. Evaluation of Cryoprotectant Composition containing a Surfactant orUrea.

The poor wetability of aqueous THFA solutions on some of the waxy-leavedplants such as peppers or tomatoes delays absorption of this solutioninto the plant tissues. In order to improve the wetability, twodifferent surfactants selected from the EPA inert compound list weretested. Both surfactants dramatically improved the cryoprotectantcomposition's wetabiltiy. Both surfactants contained potential knowncryoprotectant ingredients such as sorbitol and polyoxyethylene. SinceTween 20 (polyoxyethylene sorbitan monolaurate) was found to mix withthe cryoprotectant composition much more easily than Tween 80(polyoxyethylene sorbitan monooleate), tween 20 was used in the frostdamage tests. Six tomatoes treated with aqueous 0.5% THFA solutionscontaining different additives were exposed to -5° C. for 4 hours. Theresults of this test are listed in Table VII. The incorporation of amere 0.1% surfactant not only dramatically improved the wetability butalso reduced the absorption time of the agent. The addition of urea didnot seem to improve the effectiveness of the agent, but the test resultsdo indicate that this agent is compatible with the fertilizer.

                  TABLE VII                                                       ______________________________________                                        FREEZING SURVIVAL TEST RESULTS FOR                                            TOMATOES EXPOSED TO -5° C. FOR FOUR HOURS                              Antifrost Agent                                                                           Additive           Results                                        ______________________________________                                        0.5% THFA   None               Survived                                       0.5% THFA   0.1% Tween 20      Survived                                       0.5% THFA   0.5% urea          Survived                                       0.5% THFA   0.5% urea + 0.1% Tween 20                                                                        Survived                                       Blank       Blank              Died                                           ______________________________________                                    

I. Evaluation of the Antifrost Agent with Peppers

In this experiment, peppers were treated with different antifrost agentsand were exposed to -6° C. for 4 hours. The test results listed in TableVIII show that the plants treated with Golden Frost Free, 0.5% THFA with0.1% Tween 20, and 0.5% THFA mixed in with 0.1% Tween 20 and 0.5% urea,survived. One interesting observation here is that 0.5% THFA did notprevent freezing damage to these plants. The reason may be the poorwetability of THFA alone on this plant. However, the effectiveness ofTHFA only on pepper plants was confirmed through additional tests.

                  TABLE VIII                                                      ______________________________________                                        FREEZING SURVIVAL TEST RESULTS FOR PEPPER                                     TREATED WITH VARIOUS ANTIFROST AGENTS AFTER                                   EXPOSURE TO -6° C. FOR 4 HOURS                                                         Conditioning/Absorption                                       Antifrost Agent Time            Results                                       ______________________________________                                        0.5% THFA       3 days/3 hours  Died                                          0.5% THFA + 0.1%                                                                              3 days/3 hours  Survived                                      Tween 20                                                                      0.5% THFA + 0.5% urea +                                                                       3 days/3 hours  Survived                                      0.1% Tween 20                                                                 0.29% Golden Frost                                                                            3 days/3 hours  Survived                                      Free                                                                          ______________________________________                                    

Further Evaluation of the Cryoprotectant Compositions with Impatiens

Freezing survival tests for impatiens were continued using aqueoussolutions of other furfuryl group compounds to evaluate theireffectiveness as antifrost agents. The impatiens used in this evaluationand in the evaluation of subpart K, infra were grown in a much warmerenvironment than the evaluations reports in subparts A-I, supra. None ofthe impatiens treated with antifrost agents and conditioned at roomtemperature for 3 to 10 days survived freezing temperatures of -3.5° C.to -6.0° C., indicating that these plants should have been acclimatizedat near freezing temperatures before they were exposed to freezingconditions.

Two impatiens were sprayed with 0.5% THFA, two with 0.5%tetrahydrofurfuryl amine, and one with 0.5% furfuryl alcohol. A controlblank was no4l treated. After standing for 7 days for conditioning,these plants were acclimated to 1° C. for 24 hours. Then the plants weresprayed once more with the respective antifrost compositions andsufficient time was allowed for the agents to be absorbed completely.Finally the plants were exposed to a temperature of -3.5° C. for 4hours. As shown in Table IX, the plants treated with THFA ortetrahydrofurfuryl amine survived whereas the others died.

                  TABLE IX                                                        ______________________________________                                        FREEZING SURVIVAL TESTS FOR IMPATIENS                                         TREATED WITH AQUEOUS                                                          SOLUTION OF FURFURYL GROUP COMPOUND AFTER                                     EXPOSURE TO -3.5° C. FOR 4 HOURS                                                     Conditioning/Acclimating/                                       Antifrost Agent                                                                             Absorption Time  Result                                         ______________________________________                                        Blank         --/24 hours/--   Died                                           0.5% THFA     7 days/24 hours/4 hours                                                                        Survived                                       0.5% THFA     7 days/24 hours/4 hours                                                                        Survived                                       0.5% Tetrahydro-                                                                            7 days/24 hours/4 hours                                                                        Survived                                       furfuryl Amine                                                                0.5% Tetrahydro-                                                                            7 days/24 hours/4 hours                                                                        Survived                                       furfuryl Amine                                                                0.5% Furfuryl Alcohol                                                                       7 days/24 hours/4 hours                                                                        Died                                           ______________________________________                                    

K. Further Evaluation of the Cryoprotectant Compositions with Impatiens

The procedure outlined in subpart J was repeated except that anotherpotential candidate, 1,2-propanediol was compared with THFA andtetrahydrofurfuryl amine. 1,2-propariediol, a polyalcohol, is the bestreported to date for its glass forming tendency and stability in theamorphous state, which are the properties required for goodcryoprotecting agents. The frost damage test results in Table X showthat tetrahydrofurfuryl alcohol and amine are better antifrost agentsthan 1,2-propanediol.

                  TABLE X                                                         ______________________________________                                        FREEZING SURVIVAL TEST RESULT FOR IMPATIENS                                   AFTER EXPOSURE TO -4° C. FOR 4 HOURS                                                 Conditioning/Acclimating/                                       Antifrost Agent                                                                             Absorption Time   Result                                        ______________________________________                                        Blank         --/24 hours/--    Died                                          0.5% 1,2-propanediol                                                                        7 days/24 hours/4 hours                                                                         Died                                          0.5% 1,2-propanediol                                                                        7 days/24 hours/4 hours                                                                         Died                                          0.5% Tetrahydro-                                                                            7 days/24 hours/4 hours                                                                         Survived                                      furfuryl Amine                                                                0.5% THFA     7 days/24 hours/4 hours                                                                         Survived                                      0.5% THFA     7 days/24 hours/4 hours                                                                         Survived                                      ______________________________________                                    

In view of the above, it will be seen that the several objects of theinvention are achieved.

As various changes could be made in the above compositions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description shall be interpreted asillustrative and not in a limiting sense.

What is claimed:
 1. A method of increasing the resistance of planttissue to damage caused by low temperature comprising applying to theplant tissue surfaces at ambient, non-freezing air temperatures at leastabout four hours prior to exposure to such low temperatures, notincluding subfreezing temperatures, an aqueous solution containing anamount of tetrahydrofurfuryl alcohol, tetrahydrofurfuryl amine ormixtures thereof effective to increase the resistance of the planttissue to such low temperatures.
 2. A method as set forth in claim 1wherein the aqueous solution contains between about 0.005 and about 25wt. % tetrahydrofurfuryl alcohol.
 3. A method as set forth in claim 1wherein the aqueous solution contains between about 0.1 and about 5 wt.% tetrahydrofurfuryl alcohol.
 4. A method as set forth in claim 1wherein the aqueous solution contains a non-ionic surfactant.
 5. Amethod as set forth in claim 4 wherein said aqueous solution containsbetween about 0.5 and 0.5 wt. % non-ionic surfactant.
 6. A method as setforth in claim 5 wherein said non-ionic surfactant is polyoxyethylenesorbitan monolaurate or polyoxyethylene sorbitan monooleate.
 7. A methodas set forth in claim 1 wherein the aqueous solution contains betweenabout 0.005 and about 25 wt. % tetrahydrofurfuryl amine.
 8. A method asset forth in claim 1 wherein the aqueous solution contains between about0.1 and about 5 wt. % tetrahydrofurfuryl amine.
 9. A method forpreventing damage to plants caused by exposure to low temperaturescomprising applying to the plant surfaces at ambient, non-freezingtemperatures at least about four hours prior to exposure to such lowtemperatures, not including subfreezing temperatures, an aqueoussolution containing an amount of tetrahydrofurfuryl alcohol effective toprevent damage to plants upon exposure to such low temperatures.
 10. Amethod as set forth in claim 9 wherein the aqueous solution containsbetween about 0.1 and about 5 wt. % tetrahydrofurfuryl alcohol.
 11. Amethod as set forth in claim 9 wherein the aqueous solution containsbetween about 0.05 and about 0.5 wt. % non-ionic surfactant.
 12. Amethod as set forth in claim 11 wherein the non-ionic surfactant ispolyoxyethylene sorbitan monolaurate or polyoxyethylene sorbitanmonooleate.
 13. A method of increasing the resistance of plant tissue todamage caused by low temperatures, including subfreezing temperatures,comprising applying to the plant tissue surfaces at ambient non-freezingair temperatures at least about four hours prior to exposure to such lowtemperatures, including subfreezing temperatures, an aqueous solutioncontaining an amount of tetrahydrofurfuryl alcohol, tetrahydrofurfurylamine or mixtures thereof effective to increase the resistance of theplant tissue to such low temperatures, including subfreezingtemperatures.
 14. A method for preventing damage to plants caused byexposure to low temperatures, including subfreezing temperatures,comprising applying to the plant surfaces at ambient non-freezingtemperatures at least about four hours prior to exposure to such lowtemperatures, including subfreezing temperatures, an aqueous solutioncontaining an amount of tetrahydrofurfuryl alcohol effective to preventdamage to the plants at such low temperatures, including subfreezingtemperatures.
 15. The method of claim 14 wherein the aqueous solutioncontains between about 0.005 and about 25 wt. % tetrahydrofurfurylalcohol.
 16. The method of claim 15 wherein the aqueous solutioncontains between about 0.1 and about 5 wt. % tetrahydrofurfuryl alcohol.17. The method of claim 14 wherein said aqueous solution furthercomprises a non-ionic surfactant.
 18. The method of claim 17 whereinsaid aqueous solution comprises between about 0.05 and about 0.5 wt. %non-ionic surfactant.
 19. The method of claim 18 wherein said non-ionicsurfactant is selected from the group consisting of polyoxyethylenesorbitan monolaurate, polyethylene sorbitan monooleate, and mixturesthereof.